The present invention relates to high-voltage circuit-breakers or to other switchgear that is insulated with a dielectric gas, and it relates more particularly to the drive rod for driving the moving contact of a circuit-breaker of a power station, which drive rod is interposed between the moving contact and the control mechanism of the circuit-breaker.
The drive rod for driving a moving contact of a high-voltage circuit-breaker in a power station generally comprises a cylindrical segment that can be either solid or hollow, and that is made of an electrically-insulating material, e.g. glass fiber reinforced with resin, and two metal endpieces fixed to respective ends of the insulating segment, one of the endpieces serving to be connected to the moving contact of the circuit-breaker, the other endpiece serving to be connected to the control mechanism.
In known manner, the metal endpiece of the rod that serves to be connected to the moving contact of the circuit-breaker is generally designed in the form of a deflector so as to protect the insulating segment of the rod from the electric arcs that strike between the contacts of the circuit-breaker during the opening operations. The deflector also serves to protect the insulating segment from the hot gases that are removed from behind the moving contact. In spite of this deflector, the insulating segment of the rod is subjected to very considerable thermal attack (burns) that can give rise to an unacceptable reduction it is dielectric strength. To protect the insulating segment from such thermal attack, consideration has already been given to surrounding it with a heat-shrinkable elastomer sheath or with stuck-on strips of PTFE (polytetrafluoroethylene). Unfortunately, with those protection techniques, it is difficult to avoid problems of air being included in the interface between the insulating segment and the protection.
An object of the invention is to provide another form of protection for such an insulating rod that is simple to implement and that does not suffer from the above-indicated drawbacks.
To this end, the invention provides a drive rod for high-voltage switchgear that is insulated with a dielectric gas, said drive rod comprising a segment made of an electrically-insulating material and two metal endpieces fixed to respective ends of the segment, wherein a thermal shield made of an electrically-insulating material is disposed between the metal endpieces and surrounds the insulating segment while being spaced apart therefrom to define an annular gap serving to be filled with dielectric gas. With this configuration, even if micro-perforations exist in the shield, there remains a thickness of dielectric gas that is not heated directly by the gas or by electrical arcing, and that thermally protects the insulating segment of the drive rod.
The shield may be made of PTFE, of a ceramic, or of some other insulating material that withstands attack from electrical arcing.
The invention also provides a circuit-breaker insulated with SF6 and equipped with a drive rod of the invention. The annular gap defined by the shield may be filled with the dielectric gas used to insulate the circuit-breaker, or with some other dielectric gas if the annular gap is completely closed.